Polycrystalline diamond material

ABSTRACT

A polycrystalline diamond material comprises a mass of diamond particles or grains exhibiting inter-granular bonding and a binder material comprising a non-metallic catalyst material for diamond, the non-metallic catalyst material for diamond being a metal oxoanion, the oxoanion being selected from the group comprising molybdates, tungstates, vanadates, phosphates and mixtures thereof.

FIELD

This disclosure relates to polycrystalline diamond (PCD) material, and to a method of making such material.

BACKGROUND

Cutter inserts for machine and other tools may comprise a layer of polycrystalline diamond (PCD) bonded to a cemented carbide substrate. PCD is an example of a superhard material, also called superabrasive material, which has a hardness value substantially greater than that of cemented tungsten carbide.

Components comprising PCD are used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. PCD comprises a mass of substantially inter-grown diamond grains forming a skeletal mass, which defines interstices between the diamond grains. PCD material comprises at least about 80 volume % of diamond and may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 GPa and temperature of at least about 1,200 degrees centigrade in the presence of a sintering aid, also referred to as a catalyst material for diamond. Catalyst material for diamond is understood to be material that is capable of promoting direct inter-growth of diamond grains at a pressure and temperature condition at which diamond is thermodynamically more stable than graphite. Some catalyst materials for diamond may promote the conversion of diamond to graphite at ambient pressure, particularly at elevated temperatures. Examples of catalyst materials for diamond are cobalt, iron, nickel and certain alloys including any of these. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for the PCD. The interstices within PCD material may at least partly be filled with the catalyst material.

A well-known problem experienced with this type of PCD material, however, is that the residual presence of the catalyst material for diamond, in particular a metallic catalyst material for diamond, for example Co, Ni or Fe, in the interstices has a detrimental effect on the performance of the PCD material at high temperatures. During application, the PCD material heats up and thermally degrades, largely due to the presence of the metallic catalyst material that catalyses graphitisation of the diamond and also causes stresses in the PCD material due to the large difference in thermal expansion between the metallic catalyst material and the diamond microstructure.

One approach to addressing this problem is to remove, typically by leaching, the catalyst material, also referred to as a catalyst/solvent in the art, from the PCD material.

U.S. Pat. No. 3,745,623 and U.S. Pat. No. 4,636,253 teach the use of heated acid mixtures in the leaching process in which mixtures of HF, HCl, and HNO₃ and HNO₃ and HF, respectively, are used.

U.S. Pat. No. 4,288,248 and U.S. Pat. No. 4,224,380 describe removal of the catalyst/solvent by leaching the PCD tables in a hot medium comprising HNO₃—HF (nitric acid and hydrofluoric acid), alone or in combination with a second hot medium comprising HCl—HNO₃ (hydrochloric acid and nitric acid).

US 2007/0169419 describes a method of leaching a portion or all of the catalyst/solvent from a PCD table by shielding the portion of the PCD table not to be leached and immersing the shielded PCD table in corrosive solution to dissolve the catalyst/solvent in water and aqua regia. The leaching process is accelerated by the use of sonic energy, which agitates the interface between the PCD table and the corrosive solution to accelerate the dissolution rate of the catalyst/solvent.

U.S. Pat. No. 4,572,722 discloses a leaching process that is accelerated by forming a hole in the PCD table by laser cutting or spark emission prior to or during the leaching process. The PCD table is then leached by using conventional acid leaching techniques, electrolytic leaching and liquid zinc extraction.

An alternative approach to addressing the problem is to use a non-metallic catalyst material for diamond that produces a more thermally stable PCD material.

JP2795738 (B2) describes sintering a mixture of diamond powder and metal carbonates at pressures of 6-12 GPa and temperatures of 1700-2500° C. to give sintered polycrystalline material consisting of 0.1-15 vol % non-metallic binder in a sintered diamond layer.

JP4114966 describes the use of carbon powder added as a sintering aid to diamond powder and an alkali earth carbonate, in order to improve the sinterability of the non-metallic system.

JP2003226578 also addresses the problem of poor sinterability, which describes the use of oxalic acid dihydrate as a sintering aid in a carbonate-based non-metallic solvent/catalyst system.

JP2002187775 describes the addition of other organic compounds to achieve a sintered carbonate-based non-metallic PCD, and similarly the addition of metal carbides is described in JP6009271.

SUMMARY

In general terms, this disclosure relates to a polycrystalline diamond material having a non-metallic catalyst material for diamond.

Viewed from a first aspect there is provided a polycrystalline diamond material comprising a mass of diamond particles or grains exhibiting inter-granular bonding and a binder material comprising a non-metallic catalyst material for diamond, the non-metallic catalyst material for diamond being a metal oxoanion, the oxoanion being selected from the group comprising molybdates, tungstates, vanadates, phosphates and mixtures thereof.

The metal oxoanion may be selected from the group of compounds of the general formula A(M_(x)O_(y))_(z) or AB(M_(x)O_(y))_(z), where A and B are alkali metals, alkali earth metals, transition metals, lanthanides, actinides, or monovalent, divalent or trivalent metals, M is tungsten, molybdenum, vanadium or phosphorous, and 0.67≦x≦4, 3≦y≦12, and 1≦z≦3.

In one or more embodiments the metal oxoanion may be selected from the group consisting of sodium molybdate, cobalt molybdate, zirconium tungstate, potassium vanadate, KBi(WO₄)₂, La₄Cu₃MoO₁₂, ZrMo₂O₈, HfW₂O₈, La₂Mo₃O₁₂, Eu₂Mo₃O₁₂, Sc_(0.67)WO₄, Eu_(0.67)MoO₄, Zr₂(WO₄)(PO₄)₂ and LnAg(WO₄)(MoO₄).

In one embodiment, the metal oxoanion is sodium molybdate.

The average particle size of the diamond particles or grains may be from about 10 nanometres to about 50 microns.

In one or more embodiments, the polycrystalline diamond material comprises residues of the binder material in the form of its oxygen- and/or nitrogen-containing compounds.

The diamond content of the polycrystalline diamond material may be at least about 80 percent, at least about 88 percent, at least about 90 percent, at least about 92 percent or even at least about 96 percent of the volume of the polycrystalline diamond material. In some embodiments, the diamond content of the polycrystalline diamond material is at most about 98 percent of the volume of the polycrystalline diamond material.

In some embodiments, the content of the non-metallic catalyst material for diamond is at most about 20 volume percent, at most about 10 volume percent, at most about 8 volume percent, or even at most about 4 volume percent of the PCD material.

A further aspect provides a method for making polycrystalline diamond material, the method including providing a mass of diamond particles or grains, contacting the diamond particles or grains with a binder material comprising a non-metallic catalyst material for diamond, the non-metallic catalyst material for diamond being a metal oxoanion, the oxoanion being selected from the group comprising molybdates, tungstates, vanadates, phosphates and mixtures thereof, consolidating the diamond particles or grains and binder material to form a green body, and subjecting the green body to a temperature and pressure at which diamond is thermodynamically stable, sintering and forming polycrystalline diamond material.

The diamond particles or grains and the binder material may be mixed in powder form with appropriate binding aids.

The diamond particles or grains and the binder material may be provided as respective adjacent layers, the non-metallic catalyst material melting and infiltrating into the layer of diamond particles or grains under suitable pressure and temperature conditions.

The diamond particles or grains may be suspended in a liquid medium, the non-metallic catalyst material for diamond precipitating in situ onto the surfaces of respective diamond particles or grains in the liquid medium in order to coat the diamond particles or grains.

Prior to contact with the binder material, the diamond particles or grains may have an average particle or grain size of from about 10 nanometres to about 50 microns.

In some embodiments, a multimodal mixture of diamond particles or grains of varying average particle or grain size are provided.

The polycrystalline diamond material may be a stand-alone compact. In other embodiments, the polycrystalline diamond material may be attached to a substrate, such as a metal carbide substrate, for example.

In one or more embodiments, the polycrystalline diamond material defines an attachment surface, and the method may include reducing non-metallic catalyst material for diamond adjacent the attachment surface to its metallic form and attaching a substrate or other supporting material to the attachment surface of the polycrystalline diamond material.

Sintering may be carried out at pressures of 6.8 GPa or more, or 7.7 GPa or more, and temperatures of 1500 degrees centigrade or more, or 2250 degrees centigrade or more, for sintering times of 3 minutes or less, or 3 minutes or longer.

Organic compounds, for example organic anhydride complexes, and/or water may also be added to aid sintering.

The non-metallic catalyst material for diamond may be removed from interstices in one or more regions of the polycrystalline diamond material to provide a polycrystalline diamond material having one or more regions substantially free of the non-metallic catalyst material for diamond.

A replacement material may be introduced into the one or more regions substantially free of the non-metallic catalyst material for diamond.

The one or more regions substantially free of the non-metallic catalyst material for diamond may be located adjacent one or more working surfaces of the polycrystalline diamond material.

Viewed from another aspect there is provided a wear element comprising a polycrystalline diamond material as described above.

Some embodiments may assist in providing one or more of enhanced thermal stability of the polycrystalline diamond material over conventional metal catalysed polycrystalline material, improved wear resistance of the polycrystalline diamond material due to precipitation hardening caused by partial decomposition of the non-metallic catalyst to form non-catalysing oxide precipitates, and improved brazing to a metal substrate by reducing the metal salt to metal at the attachment surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments will now be described with reference to the accompanying FIG. 1 which shows an XRD analysis of a sample of an embodiment of a polycrystalline diamond material.

DETAILED DESCRIPTION OF EMBODIMENTS

As used herein, “polycrystalline diamond” (PCD) material comprises a mass of diamond grains, a substantial portion of which are directly inter-bonded with each other and in which the content of diamond is at least about 80 volume percent of the material. In some embodiments of PCD material, interstices between the diamond grains may at least partly be filled with a binder material comprising a non-metallic catalyst material for diamond.

As used herein, “non-metallic catalyst material for diamond” is a material that is capable of catalysing intergrowth of polycrystalline diamond particles or grains under conditions of temperature and pressure at which diamond is more thermodynamically stable than graphite.

As used herein, “interstices” or “interstitial regions” are regions between the diamond grains of PCD material.

A multi-modal size distribution of a mass of grains is understood to mean that the grains have a size distribution with more than one peak, each peak corresponding to a respective “mode”. Multimodal polycrystalline bodies are typically made by providing more than one source of a plurality of grains, each source comprising grains having a substantially different average size, and blending together the grains or particles from the sources. Measurement of the size distribution of the blended grains typically reveals distinct peaks corresponding to distinct modes. When the grains are sintered together to form the polycrystalline body, their size distribution is further altered as the grains are compacted against one another and fractured, resulting in the overall decrease in the sizes of the grains. Nevertheless, the multimodality of the grains is usually still clearly evident from image analysis of the sintered article.

As used herein, a green body is an article that is intended to be sintered or which has been partially sintered, but which has not yet been fully sintered to form an end product. It may generally be self-supporting and may have the general form of the intended finished article.

As used herein, a superhard wear element is an element comprising a superhard material and is for use in a wear application, such as degrading, boring into, cutting or machining a workpiece or body comprising a hard or abrasive material.

A polycrystalline diamond material according to some embodiments comprises diamond having increased thermal stability over conventional solvent/catalyst sintered diamond composite materials. In some embodiments, the polycrystalline diamond material includes a binder comprising a non-metallic catalyst material for diamond. The non-metallic catalyst material for diamond may be a metal oxoanion, wherein the oxoanion is selected from the group comprising the molybdates, tungstates, vanadates, phosphates and mixtures thereof.

In some embodiments, the metal oxoanions include compounds of the general formula A(M_(x)O_(y))_(z) or AB(M_(x)O_(y))_(z), where A and B are alkali metals, alkali earth metals, transition metals, lanthanides, actinides, or monovalent, divalent or trivalent metals, M is tungsten, molybdenum, vanadium or phosphorous, and 0.67≦x≦4, 3≦y≦12, and 1≦z≦3.

Although not an exhaustive list, exemplary metal oxoanions may include sodium molybdate, cobalt molybdate, zirconium tungstate, potassium vanadate, KBi(WO₄)₂, La₄Cu₃MoO₁₂, ZrMo₂O₈, HfW₂O₈, La₂Mo₃O₁₂, Eu₂Mo₃O₁₂, Sc_(0.67)WO₄, Eu_(0.67)MoO₄, Zr₂(WO₄)(PO₄)₂ and LnAg(WO₄)(MoO₄).

A method for making polycrystalline diamond material, in some embodiments, includes contacting a mass of diamond particles or grains with a binder material comprising a non-metallic catalyst material for diamond. The non-metallic catalyst material for diamond may be a metal oxoanion, the oxoanion being selected from the group comprising the molybdates, tungstates, vanadates, phosphates and mixtures thereof. The diamond particles or grains and binder material may be consolidated into a green body, which green body is then subjected to a temperature and pressure at which diamond is more thermodynamically stable than graphite in order to sinter it and form polycrystalline diamond material.

In some embodiments, the non-metallic binder material is combined with the diamond particles or grains in powder form and mixed in a conventional mixing process such as, for example, a planetary ball milling process, typically in the presence of a milling aid such as methanol, for example. Milling balls, such as Co—WC milling balls, are used to mill the binder and diamond powders together. The binder and diamond mixture is then typically dried at a temperature of 50 to 100° C. to remove the methanol and other volatile residues. It is then consolidated into a green body ready for sintering. Alternatively, the diamond powder and binder material may be provided in layer form, the non-metallic catalyst material for diamond melting and infiltrating into the diamond powder layer under suitable temperature and pressure conditions, as would be appreciated by a person skilled in the art.

In an alternative embodiment, the non-metallic binder material is combined with the diamond particles or grains in a sol-gel process. Diamond powder is suspended in a liquid under vigorous stirring to form a diamond suspension. The liquid is typically water although the person skilled in the art will appreciate that any appropriate liquid medium may be used. A first salt of the desired oxoanion is chosen such that it is soluble in a solvent, but forms an insoluble salt with a chosen cation in the diamond suspension. A second salt of the desired cation is chosen such that it is soluble in a solvent, but the cation forms an insoluble salt with the oxoanion of the first salt.

The two salt containing solutions are added concomitantly drop wise to the diamond suspension such that an insoluble precipitate comprising a molybdate, tungstate, vanadate, phosphate, or mixture thereof, forms on the surface of the respective diamond particles or grains.

The liquid containing the suspended diamond particles or grains is stirred during the drop wise addition. This stirring may be accomplished by a heater-stirrer and magnetic stirrer, or by an overhead stirrer, or by ultrasonication, or any other suitable method that is able effectively to disperse the diamond particles in the liquid.

The diamond powder with precipitated salt may be removed from suspension and dried at a temperature suitable for removing any residual suspension medium or solvents that may be present. The drying temperature is typically 50 to 100° C. The diamond with precipitated salt may be stationary during drying, or may be agitated, tossed or moved in a way that increases the efficiency or rate of drying. The diamond particles and binder material are consolidated to form a green body.

Prior to contact with the binder material, the diamond particles may have an average particle size ranging from about 10 nanometres to about 50 microns.

The green body, once formed is placed in a suitable container and introduced into a high pressure high temperature press. Pressure and heat are applied in order to sinter the diamond particles together, typically at pressures of 6.8 to 7.7 GPa or more and temperatures of 1500 to 2200° C. or more.

In one embodiment, the metal salt adjacent a surface of the polycrystalline diamond material is reduced to its metal, by for example reacting with dry hydrogen at elevated temperature, which is expected to facilitate brazing of the polycrystalline diamond material onto a metal carbide substrate, for example.

EXAMPLES

Some embodiments are described in more detail with reference to the examples below, which are not intended to be limiting.

Example 1 Fine Diamond with Sodium Molybdate Admixed by Planetary Ball Milling

25 g of diamond powder of approximate average particle size 20 microns was added to 125 g of Co—WC milling balls in a polypropylene milling jar of approximate volume 600 ml. 2.5 g of anhydrous sodium molybdate and 100 ml of methanol were added, the jar was sealed and placed in a planetary ball mill and milled for 15 minutes at 90 rpm. The milling jar was opened, and a further 25 g of the diamond powder was added along with a further 125 g of milling balls, a further 2.5 g of sodium molybdate and 100 ml of methanol. The jar was sealed and milled for a further 15 minutes at 90 rpm. The milling jar was removed from the mill, opened and left in an oven at 50 degrees centigrade overnight for the methanol to evaporate and the diamond-salt powder mix to dry.

The diamond-salt mix was separated from the milling balls by screening, then 2 g of the mix was placed in a metal canister and sintered at 7.7 GPa and 2250 degrees centigrade for 3 minutes. SEM analysis of the sintered PCD material showed intergrowth between the diamond grains. XRD analysis of the sintered PCD material, as depicted in FIG. 1, showed the presence of MoO₂ and Na_(0.9)Mo₂O₄, with traces of NaWO₃, the tungsten having been introduced due to contamination by the Co—WC milling balls during the milling step. A wear test showed an improvement of approximately 20% over similar metallic PCD containing Co—WC binder. Thermogravimetric analysis showed an increase in the temperature of oxidation from 750 degrees centigrade for the standard metallic PCD to 940 degrees centigrade for the non-metallic PCD, indicating a significant improvement in the thermal stability of the latter.

Example 2 Fine Diamond with Colloidally Deposited Cobalt Molybdate

65 g of diamond powder of average particle size 2 micron may be suspended in 2.5 litres of deionised water. An aqueous solution of cobalt nitrate, Co(NO₃)₂, and an aqueous solution of sodium molybdate, NaMoO₄, may be added simultaneously and dropwise to the suspension while vigorously stirring the suspension. The cobalt nitrate solution may be made by dissolving 35 g of Co(NO₃)_(2.6)H₂O in 200 ml of deionised water. The sodium molybdate solution may be made by dissolving 30 g of NaMoO₄ in 200 ml of deionised water. The cobalt nitrate and sodium molybdate may be reacted to form a precipitate of cobalt molybdate on the surfaces of the suspended diamond particles. The diamond powder with cobalt molybdate precipitate may be washed, typically twice with deionised water, to remove the soluble sodium nitrate by-product of the reaction.

The coated diamond may be washed in ethanol, and dried in an oven overnight at 50 degrees centigrade. A 2 g sample of the dried coated diamond may be placed in a metal canister and sintered at 7.7 GPa and 2250 degrees centigrade for 3 minutes. SEM analysis of the sintered PCD is expected to show diamond intergrowth, with a more homogeneous microstructure than was obtained in Example 1 by milling. Similar benefits with respect to wear behaviour and thermal stability as obtained in Example 1 are expected.

Example 3 Fine Diamond with Colloidally Deposited Zirconium Tungstate

65 g of diamond powder of average particle size 2 micron may be suspended in 2.5 litres of deionised water. An aqueous solution of zirconium nitrate, Zr(NO₃)_(4.5)H₂O, and an aqueous solution of potassium tungstate, K₂WO₄, may be added simultaneously and dropwise to the suspension while vigorously stirring the suspension. The zirconium nitrate solution may be made by dissolving 54 g of Zr(NO₃)_(4.5)H₂O in 200 ml of deionised water. The potassium tungstate solution may be made by dissolving 52 g of K₂WO₄ in 200 ml of deionised water. The zirconium nitrate and potassium tungstate may be reacted to form a precipitate of zirconium tungstate on the surfaces of the suspended diamond particles. The diamond powder with zirconium tungstate precipitate may be washed, typically twice with deionised water, to remove the soluble potassium nitrate by-product of the reaction.

The coated diamond may be washed in ethanol, and dried in an oven overnight at 50 degrees centigrade. A 2 g sample of the dried coated diamond may be placed in a metal canister and sintered at 7.7 GPa and 2250 degrees centigrade for 3 minutes. SEM analysis of the sintered PCD is expected to show diamond intergrowth, with a more homogeneous microstructure than was obtained in Example 1 by milling. Similar benefits with respect to wear behaviour and thermal stability as obtained in Example 1 are expected.

Example 4 Fine Diamond With Potassium Vanadate Admixed by Planetary Ball Milling

25 g of diamond powder of approximate average particle size 20 microns may be added to 125 g of Co—WC milling balls in a polypropylene milling jar of approximate volume 600 ml. 3 g of tripotassium vanadate, K₃VO₄, and 100 ml of methanol may be added, the jar sealed and placed in a planetary ball mill and milled for 15 minutes at 90 rpm. On opening the milling jar, a further 25 g of the diamond powder may be added along with a further 125 g of milling balls, a further 3 g of tripotassium vanadate and 100 ml of methanol, followed by sealing the jar and milling for a further 15 minutes at 90 rpm. Drying may be achieved by removing the milling jar from the mill, opening and leaving in an oven at 50 degrees centigrade overnight for the methanol to evaporate and the diamond-salt powder mix to dry.

The diamond-salt mix may be separated from the milling balls by screening, then 2 g of the mix may be placed in a metal canister and sintered at 7.7 GPa and 2250 degrees centigrade for 3 minutes. A wear test is expected to show an improvement over similar metallic PCD containing Co—WC binder. 

1. A polycrystalline diamond material comprising a mass of diamond particles or grains exhibiting inter-granular bonding and a binder material comprising a non-metallic catalyst material for diamond, the non-metallic catalyst material for diamond being a metal oxoanion, the oxoanion being selected from the group comprising molybdates, tungstates, vanadates, phosphates and mixtures thereof.
 2. A polycrystalline diamond material according to claim 1, wherein the metal oxoanion is selected from the group of compounds of the general formula A(M_(x)O_(y))_(z) or AB(M_(x)O_(y))_(z), where A and B are alkali metals, alkali earth metals, transition metals, lanthanides, actinides, or monovalent, divalent or trivalent metals, M is tungsten, molybdenum, vanadium or phosphorous, and 0.67≦x≦4, 3≦y≦12, and 1≦z≦3.
 3. A polycrystalline diamond material according to claim 1, wherein the metal oxoanion is selected from the group comprising sodium molybdate, cobalt molybdate, zirconium tungstate, potassium vanadate, KBi(WO₄)₂, La₄Cu₃MoO₁₂, ZrMo₂O₈, HfW₂O₈, La₂Mo₃O₁₂, Eu₂Mo₃O₁₂, Sc_(0.67)WO₄, Eu_(0.67)MoO₄, Zr₂(WO₄)(PO₄)₂ and LnAg(WO₄)(MoO₄).
 4. A polycrystalline diamond material according to claim 1, wherein the metal oxoanion is sodium molybdate.
 5. A polycrystalline diamond material according to claim 1, wherein the diamond particles have an average particle or grain size of from about 10 nanometres to about 50 microns.
 6. A polycrystalline diamond material according to claim 1, wherein the diamond content of the polycrystalline diamond material is at least 80 percent and at most 98 percent of the volume of the polycrystalline diamond material.
 7. A polycrystalline diamond material according to claim 1, wherein the polycrystalline diamond material comprises at most 20 volume percent of the non-metallic catalyst material for diamond.
 8. A method for making polycrystalline diamond material, the method including providing a mass of diamond particles or grains, contacting the diamond particles or grains with a binder material comprising a non-metallic catalyst material for diamond, the non-metallic catalyst material for diamond being a metal oxoanion, the oxoanion being selected from the group comprising the molybdates, tungstates, vanadates, phosphates and mixtures thereof, consolidating the diamond particles or grains and binder material to form a green body, and subjecting the green body to a temperature and pressure at which diamond is thermodynamically stable, sintering and forming polycrystalline diamond material.
 9. A method according to claim 8, wherein the metal oxoanion is selected from the group of compounds of the general formula A(M_(x)O_(y))_(z) or AB(M_(x)O_(y))_(z), where A and B are alkali metals, alkali earth metals, transition metals, lanthanides, actinides, or monovalent, divalent or trivalent metals, M is tungsten, molybdenum, vanadium or phosphorous, and 0.67≦x≦4, 3≦y≦12, and 1≦z≦3.
 10. A method according to claim 8, wherein the metal oxoanion is selected from the group comprising sodium molybdate, cobalt molybdate, zirconium tungstate, potassium vanadate, KBi(WO₄)₂, La₄Cu₃MoO₁₂, ZrMo₂O₈, HfW₂O₈, La₂Mo₃O₁₂, Eu₂Mo₃O₁₂, Sc_(0.67)WO₄, Eu_(0.67)MoO₄, Zr₂(WO₄)(PO₄)₂ and LnAg(WO₄)(MoO₄).
 11. A method according to claim 8, wherein the metal oxoanion is sodium molybdate.
 12. A method according to claim 8, wherein the method includes subjecting the green body in the presence of the non-metallic catalyst material for diamond to a pressure and temperature at which diamond is more thermodynamically stable than graphite.
 13. A method according to claim 12, wherein the pressure is at least about 6.8 GPa and the temperature is at least about 1500 degrees centigrade.
 14. A method according to claim 8, wherein the formed polycrystalline diamond material defines an attachment surface, the method including reducing non-metallic catalyst material for diamond adjacent the attachment surface to its metallic form and attaching a substrate or other supporting material to the attachment surface of the polycrystalline diamond material.
 15. A wear element comprising a polycrystalline diamond material according to claim
 1. 